The long term objective is to quickly and accurately measure infant volume in air so that the deduced rate of increase in lean-body mass can be correlated with the infant diet. Such routine measurements of body density should result in improving diet programs that reduce infant hospital confinement and mortality rate. Known devices for the measurement of infant body volume in air are subject to inaccuracies and long measurement times because the infants presence tends to increase the temperature and humidity. Air displacement and simple Helmholtz resonator schemes are sensitive to such changes. The proposed new device uses acoustic resonance principles that are expected to eliminate problems related to temperature and humidity changes. It is expected that very accurate measurements can be made in much less than a minute with inexpensive instrumentation that reads out the body-volume, density and estimated lean-body mass. The device should be inexpensive to manufacture and a product desired and eventually required by every hospital and clinic.